1. Field of the Invention
The present invention relates to circularly polarized wave antennas for transmitting/receiving circularly polarized radio waves and wireless apparatus using the same.
2. Description of the Related Art
In FIG. 12A, an example of a conventional circularly polarized wave antenna included in a wireless apparatus is schematically shown. In FIG. 12B, a sectional view taken along the line a--a of FIG. 12A is shown. A circularly polarized wave antenna 1 shown in FIGS. 12A and 12B includes a dielectric member 2 of a rectangular prism shape. On the top surface of the dielectric member 2, a circular radiative electrode 3 is formed. Also, the dielectric member 2 is provided with through holes from the top surface to the bottom surface. Feed pins P are inserted into the through holes. The feed pins P are formed such that electrical power is supplied thereto from the outside. When electrical power is supplied from the outside to the radiative electrode 3 through the feed pins P, the radiative electrode 3 is excited in, for example, two directions, i.e., the a--a axis direction and the b--b axis direction (specifically, the direction intersecting the a--a axis direction at an angle of 45.degree.), as shown in FIG. 12A.
The circularly polarized wave antenna 1 shown in FIGS. 12A and 12B can transmit/receive circularly polarized radio waves by exciting the radiative electrode 3, as described above.
With the construction shown in FIGS. 12A and 12B, when the relative dielectric constant of the dielectric member 2 is increased so as to miniaturize the circularly polarized wave antenna 1, and therefore the dielectric member 2, the axial ratio deteriorates when the circularly polarized wave antenna 1 is operated in a higher mode.
As described above, the circularly polarized wave antenna 1 is structured such that the radiative electrode 3 is excited in two directions meeting at a 45.degree. angle. As shown in FIGS. 12A and 12B, when the radiative electrode 3 is formed on the top surface of the rectangular-prism dielectric member 2, for example, a spacing d1 in the a--a axis direction between an outer peripheral edge of the dielectric member 2 and an edge of the radiative electrode 3 is greater than a spacing d2 in the b--b axis direction between an outer peripheral edge of the dielectric member 2 and an edge of the radiative electrode 3. Hence, the spacing between the outer peripheral edge of the dielectric member 2 and the edge of the radiative electrode 3 is different for each excitation direction of the radiative electrode 3. As described above, when the relative dielectric constant of the dielectric member 2 is high, the difference in the spacing causes differences in edge effects, thus failing to match the resonant frequencies of the two excitation directions in the radiative electrode 3. As a result, a problem arises in that the axial ratio deteriorates when the circularly polarized wave antenna 1 is operated in a higher mode.
The circularly polarized wave antenna shown in FIGS. 12A and 12B is structured such that electrical power is supplied to the discharge electrode 3 using the feed pins P so as to excite the discharge electrode 3. When the feed pins P are used in this manner, it is difficult to match the resonant frequencies of the two excitation directions in the radiative electrode 3.
In addition, the circularly polarized wave antenna shown in FIGS. 12A and 12B has problems as described below. A circuit board on which the circularly polarized wave antenna 1 is to be mounted is provided with a circuit section for driving the circularly polarized wave antenna 1. In order to miniaturize the circuit board, the circuit section is occasionally disposed on the surface opposite to the surface on which the circularly polarized wave antenna 1 is to be mounted. In the circularly polarized wave antenna 1 shown in FIGS. 12A and 12B, the feed pins P are disposed near the center of the dielectric member 2. As described above, when the circuit section is provided on the opposite side of the circuit board, it is difficult to satisfactorily provide a conductive connection between the feed pins P of the circularly polarized wave antenna 1 and the circuit section. Also, patterning of the circuit section is difficult.